1. Field of the Invention
The present invention relates to an endoscope for medical use.
2. Description of the Related Art
Generally, an endoscope for medical use comprises an insertion section and an operation section. The insertion section is designed to be inserted into a patient's body cavity. The operation section is coupled to the proximal end of the insertion section.
FIGS. 41A and 41B are front and sectional views of the distal portion (a) of the insertion section of the endoscope disclosed in Japanese UM Appln. KOKAI Publication No. 64-36816. As seen from FIGS. 41A and 41B, the distal portion (a) has front (b), in which an illumination window section (c) and an observation window section (e) are provided. The illumination window section (c) incorporates an illumination lens (d). The observation window section (e) incorporates an observation lens (f), a washing nozzle (g), a forceps channel (h) and the like.
As shown in FIG. 41B, the front (b) of the distal portion (a) is rounded. The observation lens (f) is fitted in the outermost part of the front (b). The light emitted through the illumination lens (d) is therefore prevented from reaching the observation lens (f). This eliminates the possibility that the image observed through the endoscope has flare or ghost. Since the front (b) is rounded, the distal portion (a) can be smoothly inserted into a body cavity.
In order to minimize the outside diameter of the distal portion (a), the illumination lens (d), observation lens (f), washing nozzle (g), forceps channel (h) and the like are arranged as close as possible to one another, as is illustrated in FIG. 41A. Consequently, the observation lens (f) is not aligned with the axis (O) of the distal portion (a). The outermost part of the rounded front (b), in which the lens (f) is fitted, is therefore located off the axis (O) namely aligned with the axis (Oe) of the observation lens (f). Consequently, the front (b) has a part (i) which has a radius of curvature less than any other part. This part (i) is more likely to be caught in the wall of a body cavity than any other part as the distal portion (a) is inserted into the body cavity. This would be a bar to smooth insertion of the insertion section.
To achieve smooth insertion of the insertion section, the front (b) of the distal portion (a) may be rounded as shown in FIG. 41D with a large radius (R) of curvature, having no part of a small radius of curvature. The front (b) can be so rounded by aligning the observation lens (f) with the axis (O) of the distal portion (a) as is shown in FIGS. 41C and 41D. If the lens (f) is aligned with the axis (O), however, the other components incorporated in the front (b), i.e., the illumination lens (d), washing nozzle (g), forceps channel (h) and the like, must be located around the observation lens (f) as shown in FIG. 41C. They are spaced apart from the lens (f) which is positioned at the center of the front (b). Consequently, the outer diameter of the distal portion (a) increases as is clearly seen from FIGS. 41A and 41B.